Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, which are suitable for an image pickup apparatus using a solid-state image pickup element, e.g., a video camera, an electronic still camera, a broadcasting camera, or a monitoring camera.
Description of the Related Art
There has been known an image pickup system including a camera main body, which includes a solid-state image pickup element, such as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), and an interchangeable lens apparatus, which includes an image pickup optical system configured to form an optical image on an image pickup sensor surface. The image pickup optical system used in the interchangeable lens apparatus is required to be a compact zoom lens having a high zoom ratio and high optical characteristics over the entire zoom range.
Moreover, such image pickup system as described above is required to be able to execute not only still image shooting but also moving image shooting. In the moving image shooting, a focusing operation, which is executed during the still image shooting, needs to be performed repeatedly. Here, during the moving image shooting, it is a common practice to use a method of detecting a direction of shift from an in-focus state by driving a focus unit to reciprocate in an optical axis direction. The operation of driving the focus unit to reciprocate in the optical axis direction is referred to as “wobbling”. In this method, during the wobbling, signal components in a particular frequency band of an image region are detected from output signals, which are obtained by an image pickup sensor, to calculate a position of the focus unit in the optical axis direction at which the in-focus state is achieved.
In the focusing operation during the moving image shooting, in order not to make a user feel a sense of discomfort, such as flickering, the focus unit needs to be driven at high speed when the focus unit is driven to wobble. When the focusing operation is performed by the wobbling, and when a weight of the focus unit is heavy, an actuator is increased in size in order to drive the focus unit at high speed. As a result, the maximum diameter of a lens barrel is increased, and the interchangeable lens apparatus is increased in size.
In order to achieve an increase in speed of the focusing operation, there has been known a telephoto-type zoom lens, which is configured to drive a lens unit arranged on an image side of an aperture stop to wobble, to thereby perform the focusing operation. In Japanese Patent Application Laid-Open No. H10-39215 and Japanese Patent Application Laid-Open No. 2009-168934, there is disclosed a zoom lens including, in order from an object side to an image side, first to fifth lens units having positive, negative, positive, positive, and negative refractive powers, in which the fifth lens unit, which is relatively compact and lightweight, is configured to function as a focus unit.
In Japanese Patent Application Laid-Open No. 2012-53444, there is disclosed a zoom lens including, in order from an object side to an image side, first to sixth lens units having positive, negative, positive, positive, positive, and negative refractive powers, in which the fifth lens unit or the sixth lens unit is configured to function as a focus unit.
In a telephoto-type zoom lens, in order to perform high-speed focusing while achieving the high zoom ratio and downsizing of the entire lens system, it is important to appropriately set a zoom type, refractive powers of respective lens units, a lens configuration, and other such factors.